The benefits of computer virtualization have been recognized as greatly increasing the computational efficiency and flexibility of a computing hardware platform. For example, computer virtualization allows multiple virtual computing machines (VMs) (or “guests”) to run on a common computing hardware platform (referred to as a “host”) even when the software components, such as the guest operating systems of each virtual machine, differ. Similar to a physical computing hardware platform, virtual computing machines include storage media, such as virtual hard disks, virtual processors, guest physical memory, virtual devices, and other system components associated with a computing environment. In a typical virtualized machine architecture, a virtual hard disk stores a guest operating system, data, and application files for a virtual machine. Virtualization software receives disk read and write requests from guest software running on the virtual machine and maps the requests to a disk image file containing an image of the virtual disk on a datastore accessible by the host. The disk image file is block-based, and contains file segments that map to disk blocks of the virtual disk. Thus, when the virtual machine reads a particular disk block, that request is mapped to a read of the corresponding segment of the disk image file, the contents of which are supplied to the virtual machine in a manner consistent with an ordinary disk read.
Server-based computing, such as available using computer virtualization architectures, allows a networked client computing system, remotely situated with respect to a server computing system, to access computing resources on the server. For example, a client computing system can use a remote desktop protocol such as Remote Desktop Protocol (RDP) Virtual Network Computing (VNC), or PCoIP to access a desktop remotely. A virtual desktop is a virtual computing system that operates as a desktop or workstation computer that an end user can interact with using the remote desktop protocol and client software and/or hardware. The client software and/or hardware transmits user input such as keyboard or mouse input to the remote system to be processed there, and receives display and other data, such as sound, for presentation to the user.
Server-based computing facilitates centralized management of computing resources. However, one drawback is that the user must have the client system remain connected to the network while accessing to the user's desktop stored on the server.
As an alternative to server-based computing, client-side computing allows the user to be located away from an enterprise network and in offline mode, i.e., not connected to a network or the Internet. From an enterprise management standpoint, however, client-side computing leads to undesirable inefficiencies when it comes to such tasks as updating operating systems and applications, enforcing security, licensing compliance, locking information, forcing adherence to various enterprise or corporate policies, and data backup.
Some of the challenges described above have been addressed by extending the server-based desktop-virtual machine architecture to a client machine by allowing a user to “check out” a virtual desktop such that it can be accessed on the client machine while offline. At the time of check out, a copy of the virtual disk of the user's virtual desktop is instantiated on the client machine and accessed by a (new) virtual machine started on the client system. The user is then able to access his or her virtual desktop without being connected to a network. Later, upon “check in,” the changes to the virtual disk are synchronized to the virtual disk maintained in the server system.
Others have addressed the above challenges by running a virtual desktop in the datacenter (on the server system) and, using a “thin” (display only) client, to cause the server system to stream down only needed portions of the virtual disk upon each access (for example, using a limited cache).
In all these cases, the actual desktop virtual disk image is provisioned, maintained, and/or monitored in the datacenter. Accordingly, all of the user content stored on the virtual disks by a virtual desktop is also maintained by the virtual computing infrastructure executing on the servers. To access the data, a user must start a virtual desktop, load or otherwise gain access to the data to perform desired functions, and then exit the virtual desktop.
In recent years, the computing experience has changed due to the wide spectrum of devices are capable of running the Internet on handheld devices. Different form factors, capacities, permissions, etc., make the delivery and running virtual desktops difficult on these devices.